Chapter 3
The Story of the Atom
Aristotle, and other Greek philosophers, did not believe
atoms existed. They believed matter was made up of four
elements: Fire, Earth, Water and Air. Their model of the four
elements looked like the image above.
The story of radioactivity must be told by going all the way
back, thousands of years, to the first philosophers and
scientists who wondered about the nature of the material
world. These early scientists did not have the tools that
Becquerel and Roentgen had. However, they did have two
essential pieces of equipment: their eyes and their minds.
Remarkably, early scientists did have ideas about the atom.
Democritus
1628 painting by Hendrik der Brugghen; copyright expired
It was a pretty good thing that Democritus could laugh,
because a lot of important people thought his ideas were a
little nutty. These people included Aristotle and Plato; Plato
wanted to burn the books Democritus had written, every one
of them.
These ideas arose in many cultures, one of them ancient
Greece.
Democritus was a philosopher and scientist born about 2500
years ago in Thrace. He was curious about the world around
him. More importantly, he questioned ideas other people had
about the nature of matter. In fact, he laughed at other
people. He did this so often that people called him The
Laughing Philosopher. Paintings of Democritus often show
him laughing, as he is doing in the portrait on the following
page.
As it turned out, Democritus' idea of the material world was
more accurate than the ideas other famous philosophers held.
Democritus believed that physical things were made up of
atoms--small, unbreakable and constant bits of matter. He
believed these small parts moved around in space,
sometimes joining together, sometimes not.
It turns out that, in a way, Democritus was correct. A more
accurate notion about the nature of atoms would not get
much clearer until the early 1800s. That was when a scientist
named John Dalton noticed a pattern in the way gasses
combined. He observed that when they came together and
separated it was always in the same proportion. He realized
that there was nothing accidental about this pattern.
From his observations Dalton concluded that each gas was
made up of an essential particle, which he called an atom.
He had read the work of Democritus and although Dalton's
idea of the atom was a little different from the ancient
philosopher's idea, still the word served its purpose.
It was curious that Dalton turned to the writings of
Democritus because, in a way, he was a little bit like the
ancient philosopher. Dalton also was someone that few
people would have expected to grow up and be a famous
scientist. He was very poor as a child. He wanted to attend a
formal school but his family could not afford it.
Friends Meeting House in Fairfield, UK
Photo by Humphrey Bolton; Creative Commons Share-Alike 2.0 Attribution license
Dalton attended a Quaker Meeting House that probably
looked a lot like the one above. It was in a neighboring
community and was built in 1689, about twenty years before
Dalton's Quaker Meeting House was built.
Dalton went instead to a local Quaker school. He made the
most of the opportunity. At the age of twelve he became a
teacher at the school.
Dalton's ambition and desire to learn served him well. By the
time he was twenty-six he had become a math and
philosophy teacher at Manchester’s New College, where he
was allowed to use the laboratory. That's all Dalton needed
to pursue his ideas. He went on to discover a number of
scientific principles. Some of these described the nature of
the atom.
After much investigation, Dalton came up with a list of
elements that he believed occurred in nature. He assigned
each of the elements a weight. He also figured out which
atoms combined, or joined together, to create chemical
combinations.
For example, Dalton observed that water was made up of
hydrogen and oxygen. When hydrogen and oxygen atoms
came together to form water, neither one lost or gained
weight. If the hydrogen and oxygen atoms broke apart, each
atom maintained the same weight as it had been before.
Dalton's discoveries about the atom laid the foundation for
other scientists' work. He is considered the founder of
modern atomic science.
John Dalton
A picture of John Dalton, by Charles Turner. Library of Congress, public domain